1. Filed of the Invention
The invention relates to a printing media type discrimination apparatus and method, and a printing apparatus.
2. Description of the Related Art
In printing apparatuses (image formation apparatuses) of electronic photographing, thermal printing, wire-dot and inkjet types that print images on the printing surface of a printing medium by adhering colored toner and ink thereto, the resulting image quantity significantly depends on the type of the printing medium. Thus, before starting image printing, a printing mode suitable for the type of the selected printing medium is set, and images are then printed in accordance with the selected printing mode.
In order to set a printing mode suitable for the selected printing medium, a variety of methods have been proposed that automatically discriminate the type of each printing medium installed in the printing apparatus.
For example, there is a method that automatically identifies the type of the printing medium, based on its transparency. In such a technique, an optic sensor sensitive to reflection and another optic sensor sensitive to transparency are individually installed in the printing media transport path. Then the opaque printing media such as plain paper are identified with the detection output from the reflection-sensitive sensor, while the transparent OHP (overhead projector) sheet (hereinafter “OHP sheet”) is identified with the detection output from the transparency-sensitive sensor.
Meanwhile, a printing-media front/rear side discriminating method is disclosed in Japanese Patent Application Laid-open No. 6-015861 (1994), for example. Provided that such a printing medium is used that has different gloss levels between its front and rear sides, the side is recognized from the difference in the gloss level.
A method to distinguish the OHP sheet from plain paper is disclosed in Japanese Patent Application Laid-open Nos. 2-056375 (1990) and 6-056313 (1994), for example. Such a method utilizes the difference in random reflection between the OHP sheet and plain paper. Namely, when the medium is irradiated with a detection light beam, the degree of random reflection on the surface is smaller in the OHP sheet than in plain paper. In this technique, a light source (light emitting device) that emits a detection light beam and a plurality of light receiving devices that receive the reflected light are installed on one side of the printing surface of the printing medium. These light receiving devices are configured to receive the regular reflection and random reflection. In such a configuration, when the intensity of regular reflection from the printing surface is large, it indicates that the printing medium is an OHP sheet. On the other hand, when the intensity of random reflection from the printing surface is large, it indicates that the printing medium is plain paper.
Furthermore, Japanese Patent Application Laid-open No. 6-056313 (1994) shows a method using a transparency-sensitive sensor and a reflection-sensitive sensor to discriminate the printing media types. In this method, a pair of light receiving devices are installed to sandwich the printing medium, and a light source emitting the detection light beam is installed on one side of the printing medium. When the printing medium comes in the light path between the light source and one of the light receiving devices installed across the printing medium, if the light receiving device does not send a detection output, the medium is decided to be plain paper. Meanwhile, if the other light receiving device sends a detection output, the medium is decided to be an OHP sheet.
Moreover, in Japanese Patent Application Laid-open No. 10-198174 (1998), a light source emitting a detection light beam and a light receiving device receiving the detection light beam reflected by the surface of the printing medium are installed, correlated with each other, so that the light path of the detection light beam makes a predetermined incident angle and a reflection angle against the surface of the printing medium. In this technique, whether the printing medium is plain paper or an OHP sheet is determined from the intensity of the regular reflection of the detection light beam that the light receiving device has received.
As an automatic printing media type discriminating method other than the above, Japanese Patent Application Laid-open No. 7-069481 (1995), for example, discloses a method utilizing a change in capacitance of the printing medium. Japanese Patent Application Laid-open No. 8-259038 (1996) discloses a method utilizing the rigidity of the printing medium.
In addition, as another automatic printing media type discriminating method, Japanese Patent Application Laid-open Nos. 6-201412 (1994) and 11-000990 (1999) disclose a method by which an identifier unique to each printing medium is installed in each printing medium and read by an optic method.
Most of the above automatic printing media type discriminating methods are, however, related to techniques for distinguishing the opaque plain paper from the transparent OHP sheet. Thus those methods have difficulty automatically discriminating a variety of media types, for example, distinguishing plain paper from coated paper with reliability.
For example, the method disclosed in Japanese Patent Application Laid-open No. 6-015861 (1994) is only applicable to printing media of which front and rear sides have different gloss levels, because it relies on the difference in the gloss level in the front and rear sides of the printing medium.
Likewise, the technique disclosed in Japanese Patent Application Laid-open Nos. 2-056375 (1990) and 6-056313 (1994) has difficulty distinguishing plain paper from coated paper because both media provide weak regular reflection of the detection light beam. As a measure to solve this problem, a plurality of thresholds may be set for signals obtained by the light receiving devices to compare and discriminate the media types. Nevertheless, because there are many types of plain paper and coated paper sharing the same threshold, it is very difficult to set a single threshold for each paper type, and thus the accuracy of media type discrimination becomes very low.
As a result, when the printing media types are identified by a conventional method relying on the transparency of the medium, only two media types—the OHP sheet or otherwise—are identified. Meanwhile, when the printing media types are identified by a conventional method relying on the gloss level, only two media types—whether glossy paper, glossy film and OHP sheet, or plain paper and coated sheet—are identified.
Even if a conventional method relying on transparency and that relying on the gloss level are combined, identified are just up to three types, namely whether the OHP sheet, or glossy media (glossy paper and glossy film) or non-glossy media (plain paper and coated paper).
On the other hand, according to the method disclosed in Japanese Patent Application Laid-open No. 10-198174 (1998), it only identifies, when the printing media are stored in a paper holder, whether the printing medium at the top is plain paper or an OHP sheet. Thus, it cannot discriminate other media types.